Effect of NAD+-dependent isocitrate dehydrogenase gene (IDH1, IDH2) disruption of sake yeast on organic acid composition in sake mash

The ratio of organic acids in sake mash is a very important factor affecting the taste of alcoholic beverages. To alter the organic acid composition in sake and investigate the mechanism of producing organic acids in sake mash, we examined the effect of NAD(+)-dependent isocitrate dehydrogenase (IDH) activity deficiency in sake yeast by disrupting the IDH1 or IDH2 gene. Two haploid strains (MATa or MAT alpha genotype) isolated from sake yeast Kyokai no. 701 (K701) were disrupted using the aureobasidin A resistant gene (AUR1-C) as a selection marker. These disruptants were defective in the activity of IDH and failed to grow on medium containing glycerol as a sole carbon source. Sake meter, alcohol concentration, and glucose consumption in sake brewed with the disruptants were reduced in comparison with those of the parental strains. The production of citrate (including isocitrate), malate, and acetate by the disruptants was increased, but succinate production was reduced to approximately half in comparison with the parental strains. These results indicate that approximately half the amount of succinate in sake mash is produced via the oxidative pathway of the TCA cycle in sake yeast. While the diploid strain constructed by mating haploid disruptants for the IDH gene exhibited stronger fermentation ability than the haploid disruptants, almost similar profiles of components in sake were obtained for both strains.